First, yes, Apple is more secure then Android. For the reasons Computerxpds said.
2nd, it's not malware you have to watch out for as much as your phone being hijacked because you gave your permission to let that app do things like change your passwords and look at your emails. Usually people would give their permission is because they didn't read what the app was asking for.
3rd, any app can do this on any OS, but apple has more security for it's apps. Also with Windows 8, there will be more windows apps and there will be cross platform apps that steal info on all user systems (PC and mobile). So it pays to know about the company and the app, not just the amount of users who downloaded it.